Device for converting sound or other vibrations into variations in an electrical circuit



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. O '0; R. MOORE. DEVICE FOR CONVERTING SOUND OR OTHER VIBRATIONS INTOVAR IAIIONS IN- AN ELECTRICAL APPLICAHON F-ILED MAY l8, 1918. V v

CHARLES R. MOORE, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELEC-TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEWYORK.

DEVICE FOR CONVERTING SOUND OR OTHER VIBRATIONS INTO VARIATIONS IN AN vELECTRICAL CIRCUIT.

Specification of Letters Patent.

Patented Apr. 19, 1921.

Application filed may 18, 1918. Serial No. 235,417.

To allwho'm. it may concern:

Be it known that I, CHARLES R. Moore, a citizen of the United States,residing at East Orange, in the county of Essex and State of New Jersey,have invented certain new and useful Improvements in Devices forConverting Sound or other Vibrations Into Variations in an ElectricalCircuit, of which the following is a full, clear, concise, and exactdescription.

This invention relates to a device for converting sound or othervibrations into variations in an electrical circuit, and moreparticularly to a device which is especially adapted to be used for thepurpose of indicating the presence and character of vibrations of soundpropagated from a distant point either through air or through water.

The device is adapted to be secured to a sound-receiving body such asthe side of a ship, a mine casing, or a diaphragm to reproducevibrations set up in such soundreceiving body in an electrical ClI'Cllltincluding an ordinary telephone receiver.

It is an object of this invention to provide a device of this characterwhich, while very sensitive, will convert the sound or other vibrationswhich it is desired to detect into variations in an electrical circuitwithout substantial distortion. It is particularly an object of theinvention to prevent distortion of vibrations of a frequency in theneighborhood of the natural frequency of the moving system of the devicedue to resonance. 1

It is also an object of this invention to provide a device of thischaracter which may be used in exposed and particularly damp placeswithout deterioration, and to provide a device which is relativelyinsensi tive to variations of local origin.

The device of the invention takes the form of a member which may besecured in fixed relation to a sound-receiving body and a second memberalso supported from said sound-receiving bodybut capable of movementrelative thereto, the inertia of said second member serving to causerelative movement betweenthe two members in response to vibrations ofthe sound-receiving body upon which the device is mounted. The relativemovement between the two members may be utilized either to vary theresistance of the electrical circuit, as in the well-known microphone,or to vary the inductance or capacity of such circuit.

In accordance with a feature of the invention, dlstortlon is preventedby supporting the relatlvely movable member by means of anenergy-absorbing material which serves to damp such relative movement,this material being of such a character as to render it resistant tomoisture. In accordance with another feature of the invention, thesupporting means is arranged so that it yields readily along a lineperpendlcular to the plane of the sound-receivmg body upon which it ismounted and possesses considerable stiffness against movement along aline parallel to such plane. In accordance with this feature of theinvention, a metal insert or stiffener is included in the yieldingsupporting means to stiffen suchsupportlng means against flexure withoutlmpalring its resiliency with reference to compression and extension.

In the embodiment of the invention disclosed herein the device takes theform of a m crophone, and more particularly of a microphone of thecarbon granule type. The device is provided with two electrodes betweenwhich is included a mass of granular carbon, such electrodes forming apart of an electrical circuit. The entire device is supported from oneelectrode and the other electrode is supported from the first electrodeby means of a member of resilient waterproof material such as rubberwhich has high energy-absorbing characteristics and which permitsrelative movement between the electrodes.

In the accompanying drawings Figure 1 represents a transverse section ofa soundrece1 ving body and the device of the inventlon supportedthereon; Fig. 2 is a rear elevation of the device.

Referring to the drawing, a sound-receiving body is indicated at 1. Asshown, it consists of a rubber diaphragm which is adapted to be suitablysupported in a situation to receive or to be actuated by sound Wavesimpinging thereon. The side of a ship or the walls of a mine casing orother submerged object may be utilized as the sound-receiving bodparticularly when the device is used for t e purpose of detecting type.Embedded in the sound-receiving body is a bushing indicated at 2, whichis.

internally threaded to receive a stem 3 which is secured to theelectrode 4. The stem 8 is adapted to be locked in the bushing by meansof a nut 5 which is threaded thereon. Also carried on the stem 3 andsurrounding an electrode 4 is a metal cup member 6 which is providedwith a circumferential ridge 7. The electrode 4, since it is mounted infixed relation with the sound-receiving body and is incapable ofmovement relative thereto, will be referred to for convenience as thefixed electrode. A second electrode 8 is secured to a disk member 9 ofmetal forming a disk structure having considerable inertia. This memberis also provided .with a circumferential ridge 10 which is formed by theperiphery of the electrode and a projection of the member 9. A ringmember 11 of comparatively soft rubber is provided with grooves whichare adapted to engage the ridges 7 and 10, so that when the ring is inposition it serves as the sole support for the electrode 8 and themember 9. The two electrodes, when assembled within the rubber ring,provide in connection with such ring, a carbon chamber which is filledwith a mass of carbon granules. The electrodes themselves may be of anysuitable construction, although they are preferably formed of carbon. Inorder to prevent short-circuiting the path throu h the granular carbon,the inner surface of t e cup member 6 may be provided with a coating ofinsulating material. The metal cup member 6 is provided withlongitudinal walls ofconsiderable extent, which walls serve to reinforcethe rubber ring 11 and thus to stiffen the rubber ring against movementparallel to the sound-receiving body.

When the device is mounted on the side of a vessel or on some othersound-receiving body, the vibrations in such sound-receiving body causethe device as a whole to vibrate.

Due, however, to the inertia of the member 8, 9 and the yieldingmounting of such mem-' her by means of the rubber ring 11, vibration ofthe sound-receiving body will set up corresponding relative movementbetween the electrodes 4 and 8. This movement varies the resistance of.the carbon granules and consequently the resistance of the electriccircuit including such carbon granules. Inasmuch as the rubbersupporting ring is of energy-absorbing material, while permitting therelative movement between the electrodes 4 and 8, it will serve to dampsuch movement and prevent undue distortion of the impulses produced inthe electrical circuit, which would occur when the system was vibratednear its natural frgqgency if no damping means were prov1 e lVhen thedevice is to be used in a special situation, particularly in a dampplace, it is desirable to exclude dampness from the carbon chamber, andthis function is also performed by the rubber ring 11, which in additionto being of energy-absorbing material, is also moistureproof. When thedevice is mounted upon a floating object and more particularly on theside of a vessel, it is subject to a considerable vibration of localorigin, due either to wave motion or to vibration of the vessel, due tothe motive power of such vessel. These vibrations, however, are ingeneral in a direction parallel with the sound-receiving body, or in adirection at right angles or transverse to the direction of soundvibrations which impinge upon such sound-receiving body. Unless thesevibrations of local origin are compensated for, noise is introduced inthe telephone receiver, due to movement of the leglcgtrodes parallelwith the sound-receiving It is apparent that in the constructiondescribed and illustrated on the drawing that the cup member 6 serves torestrain the yielding annulus 11 against flexure. In devices of thecharacter described, where an inertia element is supported by means of ayielding support from a sound responsive body at the movement of-thedevice the line with the vibration responsive body will have a tendencyto flex or bend the ylelding support. The situation is somewhatanalogous to the weight on the end of a spiral spring. In accordancewith the present invention, however, this tendency to flex or bend iscounteracted by means of the side walls of the member 6 by virtue ofwhich any motion between the inertia member 9 and the front electrode 4,parallel to each other, is restrained to a material extent, the onlymotion of this character possible being due to a slight yield in atransverse direc- ,tion of a very small length of the .tubular saidgrooves by the elasticity of the walls,

and variable resistance material included between sa1d electrodes' 3. Amicrophone compris nga rece' tacle having yielding side walls, a pair 0electrodes supported from said side walls in spaced relation, variableresistance material included between said electrodes, and means forstifi'eningsaid side walls against flexure.

4. A microphone comprising a metal cup, an electrode mounted within saidcup, an external ridge on said cup, an inertia member of considerable'mass, a second electrode carried by said inertia member, a supportingmember of yielding energy absorbing material engaging said r'idge forsupporting 10 said member on said cup, and a variable resistanceincluded between said electrodes.

In witness whereof, I hereunto subscribe my name this 13th day of May,A. D. 1918.

. CHAS. R. MOORE.

